Component alignment is of critical importance in semiconductor and/or MEMS (micro electromechanical systems) based optical system manufacturing. The basic nature of light requires that light generating, transmitting, and modifying components must be positioned accurately with respect to one another, especially in the context of free-space-optical systems, in order to function properly and effectively in electro-optical or all optical systems. Scales characteristic of semiconductor and MEMS necessitate sub-micron alignment accuracy.
Consider the specific example of coupling a semiconductor diode laser, such as a pump laser, to a fiber core of a single mode fiber. Only the power that is coupled into the fiber core is usable to optically pump a subsequent gain fiber, such as a rare-earth doped fiber or regular fiber, in a Raman pumping scheme. The coupling efficiency is highly dependent on accurate alignment between the laser output facet and the core; inaccurate alignment can result in partial or complete loss of signal transmission through the optical system.
Moreover, such optical systems require mechanically robust mounting and alignment configurations. During manufacturing, the systems are exposed to wide temperature ranges and purchaser specifications can explicitly require temperature cycle testing. After delivery, the systems can be further exposed to long-term temperature cycling and mechanical shock.
Solder joining and laser welding are two common mounting techniques. Solder attachment of optical elements can be accomplished by performing alignment with a molten solder joint between the element to be aligned and the platform or substrate to which it is being attached. The solder is then solidified to xe2x80x9clock-inxe2x80x9d the alignment. In some cases, an intentional offset is added to the alignment position prior to solder solidification to compensate for subsequent alignment shifts due to solidification shrinkage of the solder. In the case of laser welding, the fiber, for example, is held in a clip that is then aligned to the semiconductor laser and welded in place. The fiber may then also be further welded to the clip to yield alignment along other axes. Secondary welds are often employed to compensate for alignment shifts due to the weld itself, but as with solder systems, absolute compensation is not possible.
Further, there are two general classes of alignment strategies: active and passive. Typically in passive alignment of the optical components, registration or alignment features are fabricated directly on the components or component carriers as well as on the platform to which the components are to be mounted. The components are then mounted and bonded directly to the platform using the alignment features. In active alignment, an optical signal is transmitted through the components and detected. The alignment is performed based on the transmission characteristics to enable the highest possible performance level for the system.
In general, according to one aspect, the invention features an optical component installation process. This process comprises lithographically patterning and etching or otherwise forming a substrate to define a structure comprising a base and an optical component interface. The optical component is then installed on this interface. The structure is installed on an optical bench and the optical component is then positioned in an optical path above that bench.
In the preferred embodiment, the optical component is installed on the interface prior to the structure being installed on the optical bench. The structure is installed on the bench preferably using a pick-and-place machine and then affixed there using some bonding process, such as solder bonding.
One problem, however, is the fact that these conventional clips or similar structures for holding the optical components are typically expensive. Moreover, it is difficult to engineer these structures with a specified mechanical behavior to facilitate the typically rigorous optical system alignment processes.
In general, according to one aspect, the invention features an optical component installation process. The process comprises lithographically defining a structure, which comprises a base and an optical component interface. Thereafter, an optical component is installed on the interface and the structure is installed on the optical bench, such that the optical component is positioned in an optical path above the bench.
In the preferred embodiment, the step of lithographically defining the structure comprises exposing a resist material with a pattern for the structure and then developing the resist material. In the preferred embodiment, the LIGA process is used in which the resist material is electroplated to form the structure and the resist material thereafter removed.
In the preferred embodiment, for one class of optical components, the optical component is installed on the interface prior to the structure being installed on the optical bench. Presently, this sequence is used when the optical component is a passive component, such as a filter or mirror, or an active component, such as a MEMs type device, such as a MEMs filter. For other classes of optical components, such as optical fibers, the structure for holding the optical fibers first installed on the optical bench and then the fiber is subsequently installed in the structure.
Presently, the structure is installed on the bench using a pick-and-place machine and affixed to the bench using solder bonding, such as eutectic solder bonding, although other processes, such as a polymeric or resin bonding and laser welding are used alternatively.
In the preferred embodiment, the structure comprises nickel or a nickel alloy, although gold and gold alloys are an alternative. Nickel has certain advantages associated with the fact that it can be easily gold plated and has desirable deformation characteristics.
In one embodiment, the optical component is affixed to the interface of the structure via solder bonding. Here again, however, other modes of attachment are used in other implementations, such as polymeric/resin bonding and laser welding.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.